Search Results (77)

Wind turbines are among the most widely adopted renewable energy systems, yet the end-of-life management of wind turbine blades remains a major challenge. The turbine blades are primarily made of glass fiber-reinforced polymers (GFRP), which are difficult to recycle without degrading their inherent structural integrity. Instead of shredding or downcycling, this study explores a reuse strategy that preserves intact laminate from decommissioned blades and repurposes them into structural beams via glue-laminated fiber-reinforced polymers (GL-FRP) assemblies. This concept was implemented using commercial GFRP for blade-derived laminates, focusing on the structural feasibility rather than material sourcing. Adhesive joints were designed as the key enabling mechanism for structural reuse and characterized under tensile loading. Building on this, the flexural performance of GL-FRP beams was investigated in horizontal and vertical configurations, yielding an ultimate load-bearing capacity of 8 kN and 20 kN, respectively. Furthermore, stress distributions obtained from experiments, finite element (FE) simulations, and analytical frameworks were evaluated and compared. The results highlight the governing role of interlaminar stress in determining structural performance and failure of the horizontal beam. The findings provide a foundational understanding of repurposing decommissioned wind turbine blades as structural elements, offering a novel strategy for material upcycling in wind energy sector and contributing to the development of circular construction solutions. Full article

The increasing global demand for clean energy has established wind power as a leading solution for sustainable electricity generation. The efficiency and reliability of wind turbines are strongly influenced by blade design, which governs both aerodynamic performance and structural integrity. In this study, a wind turbine blade based on the National Advisory Committee for Aeronautics (NACA) 4412 airfoil was developed for composite manufacturing, with variations in laminate layers (4, 8, 12, and 16) to optimize stiffness, strength, and weight. To reduce prototyping costs and development time, the structural response under operational loads was simulated using ANSYS Workbench 2025 R1. The Taguchi method was employed to minimize the number of experimental trials, considering three factors at four levels each. A multi-objective optimization was then performed to minimize tip deformation and maximum stress while ensuring a safe failure index. The results indicated that force distance was the most influential factor, followed by laminate configuration, while force magnitude had a comparatively smaller effect within the tested range. The configuration with a force of 15 N, a force distance of 60 cm, and 12 laminate layers achieved a composite desirability of 0.9413, leading to a significant reduction in deformation and stress while maintaining structural safety. These findings validate the effectiveness of the proposed design and optimization framework and provide practical guidelines for the development of high-performance composite wind turbine blades. Full article

The study focuses on the infrared nondestructive detection of inclusion-type internal defects in glass-fiber-reinforced plastic (GFRP) wind turbine blade specimens, which were designed to simulate the laminated material structure and typical hidden defects of in-service blades. To address the difficulty of detecting internal defects in in-service wind turbine blades, this paper establishes an active thermal imaging defect detection and recognition system using a halogen lamp as the infrared thermal excitation source and a high-resolution thermal imaging camera as the detection component. To improve the recognition of defect contour information in infrared images, a method combining bidimensional filtering empirical mode decomposition (BFEMD), Gaussian filtering, and Otsu threshold segmentation is proposed. The BFEMD procedure decomposes the infrared image into bidimensional intrinsic mode function components and residual components, Gaussian filtering suppresses noise in the selected components, and Otsu threshold segmentation extracts the defect contours. Experimental results show that the combined algorithm can enhance defect targets in infrared images, improve visibility and contour integrity, and provide a higher detection rate for wind turbine blade defects under different defect depths and materials. Full article

The global expansion of wind energy increases the need for sustainable recycling strategies for glass fiber-reinforced plastic (GFRP) from end-of-life wind turbine blades (WTB). Mechanical recycling is currently the most economically and ecologically viable technology. This study compares post-industrial (PI) waste from laminate cutoffs and post-consumer (PC) GFRP waste from end-of-life WTBs to investigate the influence of waste origin, pretreatment of shredded GFRP, different particle sizes and various matrix formulations on the tensile modulus and tensile strength of pressed bulk molding compounds produced with virgin epoxy resin. Thermogravimetric analysis showed a fiber content of up to 70 wt.%, but the resin residues on the embedded glass fibers dimmish a sufficient bonding of the new matrix system. Finer GFRP fractions consistently yielded higher tensile modulus and strength, with PI and pretreated PC materials performing best. The findings of this study demonstrate that controlled particle size distribution, impurity removal and optimized resin viscosity are key factors to achieve reliable mechanical performance and enable high-value recycling routes for glass fiber composite waste. Full article

A sandwich structure consists of a light core and two thin laminates bonded on both sides of the core. Sandwich structures have applications in structural constructions such as wind turbine blades and marine boats. These structures may experience low-velocity impacts from maintenance operations or during service conditions; thus, it is important to study these low-velocity impacts. In the current study, a sandwich structure was fabricated from PVC foam core and unidirectional glass fibres using the vacuum resin infusion method. The PVC foam core used was of 10–20 mm thickness while the face sheet had two different thicknesses. The panel was tested for impact strength using drop weight equipment at impact energies at three energy levels. The results were reported for damage area, force–time, force–displacement and energy–time curves. Full article

Polymer nanocomposites offer significant potential for improving the strength-to-weight ratio and dynamic behavior of drone blades. This study examines the vibration characteristics of tapered aramid (Kevlar)/epoxy composite blades reinforced with nanocarbon fillers—graphene (2D), multi-walled carbon nanotubes (MWCNTs, 1D), and fullerene (0D)—to determine the most effective filler for enhancing stiffness and operational stability. The laminated blades (300 mm length, 200 mm width, root thickness 13 mm, tip thickness 8 mm) incorporate ply drop-offs and a central honeycomb core. Modeling was performed using classical laminate plate theory integrated with the finite element method (FEM) in MATLAB (R2016a). Under clamped–free–free–free boundary conditions, the study considered rotational speeds of 750–2250 rpm, setting angles of 30–60°, various fiber orientations, and nanofiller contents of 0–10 wt.%. The results indicate that while the setting angle minimally affects natural frequency, it significantly influences damping in modes (1,2) and (2,1). Increasing nanofiller content improves stiffness, with optimal performance observed near 5 wt.%. At 1500 rpm in mode (1,1), MWCNTs provided the greatest enhancement. Overall, MWCNTs exhibited superior stiffness improvement and rotational stability compared to other fillers. Full article

The structural segmentation of wind turbine blades offers advantages in transportation, manufacturing, and maintenance; however, it introduces interfaces that may compromise load transfer and fatigue performance. This study presents the experimental and numerical validation of a composite coupling system designed for small wind turbine blades compliant with IEC 61400-2 requirements. A 2 m representative section extracted from the mid-span region of a 9 m blade was manufactured using vacuum-assisted resin infusion and tested under static loading conditions. A detailed finite element model based on classical laminate theory and orthotropic material properties was developed to predict structural response. Experimental measurements showed a maximum tip deflection of 15 mm under the applied load, compared to 13.76 mm predicted numerically, corresponding to a deviation of 8.9%. Surface strain measurements obtained from eight strain gauges installed across the blade–coupling interface indicated maximum mean values of +632.4 με in tension and −664.2 με in compression, with no evidence of localized strain amplification at the instrumented locations. These findings demonstrate that fully composite permanent segmentation can preserve stiffness continuity while maintaining strain levels below reported fatigue initiation thresholds, supporting the structural feasibility of segmented blade architectures for small wind turbine applications. Full article

Natural fiber-reinforced polymer composites have been increasingly investigated for sustainable structural applications, including small wind turbine blades operating under low wind-speed conditions. However, despite their environmental advantages, there is a lack of experimental validation of structural models applied to real aerodynamic blade geometries manufactured with carded natural fibers, whose intrinsic fiber dispersion and microstructural heterogeneity challenge classical laminate-based approaches. The objective of this study is to evaluate the structural performance, modeling validity, and manufacturing feasibility of a small wind turbine blade produced from polyester resin reinforced with carded jute fibers, combining Classical Laminate Theory (CLT), additive-manufactured tooling, vacuum infusion processing, and quasi-static bending experiments. A 3D-printed ABS mold was used to manufacture an S1210 aerodynamic profile, enabling a low-cost and rapid tooling approach aligned with current trends in digital composite prototyping. The blade was structurally modeled using CLT with elastic properties obtained from previous experimental characterization and was experimentally evaluated through quasi-static bending tests instrumented with strain gauges at three spanwise stations. Numerical predictions showed strong agreement with experimental strain measurements, validating the applicability of CLT to carded natural-fiber laminates despite their inherent angular dispersion and microstructural variability. All monitored regions exhibited fully linear elastic behavior, with maximum stresses of approximately 5 MPa—well below the composite tensile strength (~60 MPa)—resulting in a safety factor close to 12. These results confirm the structural reliability, manufacturing feasibility, and sustainability potential of jute-reinforced polyester composites for small wind turbine blades operating in low-wind-speed environments (<2 m/s). Full article

The aim of this study is to experimentally evaluate the damage mechanisms occurring in the adhesive-bonded regions of glass fiber-reinforced polymer (GFRP) and carbon fiber-reinforced polymer (CFRP) composites, which are widely used in marine and offshore wind turbine applications, under environmental conditions. In particular, this study focuses on the degradation caused by long-term seawater exposure and its effects on the bending behavior and load-carrying capacity of adhesive joints. For this purpose, the specimens were prepared in accordance with ASTM D5868-01, using 7-layer GFRP and 8-layer CFRP laminates. Single-lap adhesive joints were fabricated. To simulate marine environmental conditions, the single-lap adhesive joints were immersed in natural seawater obtained from the Aegean Sea (22 °C temperature and 3.3–3.7% salinity) for 1, 2, and 3 months in separate containers. Three-point bending (3PB) tests were performed on specimens representing marine applications, while four-point bending (4PB) tests were conducted on specimens representing offshore wind turbine blade structures. The results quantitatively revealed the influence of seawater on adhesive-bonded composite joints. In 3PB tests, the reductions in the Young’s modulus of GFRP specimens after 1, 2, and 3 months of exposure were measured as 5.94%, 8.90%, and 12.98%, respectively. For CFRP specimens, degradation was more limited, with corresponding reductions of 1.28%, 3.39%, and 3.74%. A similar trend was observed in 4PB tests representing offshore wind turbine applications, where GFRP joints exhibited modulus reductions of 3.15%, 6.42%, and 9.45%, while CFRP joints showed reductions of 1.29%, 2.62%, and 3.48% for the same exposure durations. Overall, the findings demonstrate that CFRP composites exhibit more stable mechanical behavior under environmental exposure, whereas GFRP structures undergo more pronounced performance losses, particularly in moisture- and salt-rich environments. These results highlight the critical importance of material selection for long-term durability in offshore composite structures. The outcomes of this study contribute to a better understanding of the damage processes occurring in composite adhesive joints under environmental conditions and provide a scientific basis for developing more reliable design and material selection strategies in both the marine and wind energy sectors. Full article

To address the manufacturing and transportation challenges of large wind turbine blades, adhesive joints in modular blades have become a research focus. This study investigates six typical adhesive joint configurations for CFRP laminates using quasi-static three-point bending experiments and cohesive-zone finite element simulations. The adhesive interface is modeled with a bilinear traction–separation law using zero-thickness cohesive elements to capture damage initiation and propagation. Among the six designs, the double-slope joint exhibits the best static performance, achieving the highest peak load of 1017.26 N and showing delayed damage evolution. The superiority of the double-slope design is further examined at the blade level via a numerical cantilever model of equal-section modular blade segments under flapwise and edgewise loading. The predicted peak loads reach 9.82 × 10⁷ N (flapwise) and 5.51 × 10⁷ N (edgewise), ranking the double-slope joint highest among the investigated configurations. The findings show that the double-slope joint improves load capacity and resistance to degradation, and reveal failure mechanisms of adhesive joints, providing theoretical support for blade structural design. Full article

In recent years, new methods to reuse, repurpose, recycle, and recover decommissioned wind turbine blades (dWTBs) have actively been developed in the wind industry. In this study, the authors address the scientific challenge of repurposing decommissioned wind turbine blades for earthwork applications, particularly as part of retaining structures. A gravity retaining structure made entirely from recycled materials is introduced, consisting of glass fibre-reinforced polymer (GFRP) composite modular units derived from dWTBs. To improve the structure’s sustainability, a mixture of typical sand and lightweight waste materials is considered for filling and backfilling of the GFRP units. In particular, two waste materials are examined—a polymer foil derived from recycled laminated glass and tyre-derived aggregate (TDA) in the form of rubber powder—which are incorporated into the sand matrix in typical dry mass proportions ranging from 2% to 32% and 5% to 20%, respectively, reflecting practical ranges considered in geotechnical backfill applications. The research involved material testing of all recyclates and their mixtures with standard sand, as well as two-dimensional finite-element (2D FE) analysis of a retaining structure using the determined material properties. To facilitate the real-world implementation of this novel technology, a structure was designed to account for ground conditions at a specific site to protect against an existing landslide. In summary, this study presents the concept of a sustainable retaining structure along with results from material tests and an initial design for implementation, supported by FE analysis of overall stability. Full article

Adhesive joint failure remains a critical limitation in the manufacturing of large wind turbine blades, where reliable and reproducible surface preparation methods are required at an industrial scale. This study systematically evaluates the effect of peel ply-induced surface morphology and chemistry on the adhesion performance of glass fiber-reinforced polymer (GFRP) laminates, explicitly examining the relationship between wettability and bonding strength. Five surface conditions were generated during vacuum-assisted resin infusion using different commercial and proprietary peel plies and a smooth mold surface. Despite significant differences in contact angle and surface energy, lap shear testing revealed no significant relationship between wettability and joint strength. Instead, surface roughness-driven mechanical interlocking and adhesive–substrate compatibility dominated performance. Compared to the smooth mold surface, twill-type peel ply–modified adherends increased shear strength by up to 3.9×, while other commercial types of peel-plies presented strength improvements between 2.7 and 3.3×. More compatible adhesive–polymer resin systems exhibited a combination of cohesive and adhesive failures, with no clear dependence on surface roughness. In contrast, when the adhesive is less compatible with the substrate, surface roughness significantly affects the adhesive response, with adhesive failure predominating. The adhesive application temperature showed no measurable effect for practical industrial use. These findings demonstrate that wettability alone is not a reliable predictor of adhesion performance for this class of substrates and confirm peel ply surface modification as a robust, scalable solution for industrial wind blade bonding. Full article

This study presents an experimental investigation of steels used in special knife applications, focusing on the interrelationship between chemical composition, microstructure, heat treatment, and mechanical properties. Four representative materials were analysed: VG10 (stainless steel with nickel-laminated edges and a VG10 core), RWL₃₄^TM (powder-metallurgical steel), laminated steel K110+N695 (with a nickel interlayer), and forge-welded steel K600+K720. The steels were characterised using OES, optical microscopy and SEM, supported by EDS for local chemical analysis. Microhardness testing was applied to individual structural regions to correlate carbide morphology, layer interfaces, and heat-treatment response with hardness values. The results reveal pronounced differences in structural homogeneity and defect occurrence. Powder-metallurgical RWL₃₄^TM exhibited the most uniform microstructure with finely dispersed Cr carbides, achieving high hardness and absence of structural defects. In contrast, laminated and forge-welded steels contained large primary carbides, carbide precipitation at grain boundaries, porous cavities, and insufficient cohesion in interlayers or weld zones, which may compromise toughness. VG10 and K110+N695 showed carbide coarsening caused by inadequate heat treatment, whereas K600+K720 revealed weld-related defects and heterogeneous phase structures. Overall, the study demonstrates the critical role of heat treatment and processing route in determining blade quality and performance. The findings provide guidance for optimising steel selection and processing technologies in advanced cutlery engineering. Full article

Small-scale wind turbines (SWTs) represent a promising solution for the energy transition and the decentralization of electricity generation in non-interconnected areas. Conventional strategies to improve SWT performance often rely on active pitch control, which, while effective at rated conditions, is too costly and complex for small systems. An alternative is passive pitch control through bend–twist coupling in the blade structure, which enables self-regulation and improved power generation. This work proposes a novel blade design methodology for a 5 kW SWT that integrates passive bend–twist coupling with conventional pitch adjustment, thereby creating a hybrid passive–active control strategy. The methodology encompasses the definition of aerodynamic blade geometry, laminate optimization via genetic algorithms combined with finite element analysis, and experimental characterization of composite materials. Aerodynamic–structural interactions are studied using one-way fluid–structure simulations, with responses analyzed through the blade element momentum method to assess turbine performance. The results indicate that the proposed design enhances power generation by about 4%. The study’s originality lies in integrating optimization, structural tailoring, and material testing, offering one of the first demonstrations of combined passive–active pitch control in SWTs, and providing a cost-effective route to improve efficiency and reliability in decentralized renewable energy systems. Full article

The dissolution kinetics in conventional nitric acid and plasma-enhanced nitric acid solvolysis of composites were investigated. Unidirectional carbon fiber epoxy laminates originating from the scar of wind turbine blades were used for the study. The carbon fiber retrieval rate was experimentally determined as a function of dissolution time and composite mass. A kinetic model, which included disintegration of the polymer matrix and the mass transport of polymer fragments to the liquid phase, was implemented to investigate the main parameters that affect the dissolution rate. The plasma enhancement and the increase of the composite mass favor the carbon fiber retrieval rate, while process time slows down the matrix dissolution rate. The composite surface in contact with the liquid, solid-to-liquid volume ratio, solubility of the polymer matrix, and disintegration and mass transport rate coefficients have a significant effect on the dissolution rate, and the rate-limiting factors were revealed and analyzed. Full article